In due time they reach, say the Isle of Wight, where they set the
pencil of the seismometer at work. But there are different ways round
the earth from Japan to the Isle of Wight, the most direct route being
across Asia and Europe; the other route across the Pacific, America, and
the Atlantic. The vibrations will travel by both routes, and the former
is the shorter of the two."
TRANSMISSIONS OF VIBRATIONS
Some brief repetition may not here be amiss as to the products of
volcanic action, of which so much has been said in the preceding
pages, especially as many of the terms are to some extent technical in
character. The most abundant of these substances is steam or water-gas,
which, as we have seen, issues in prodigious quantities during every
eruption. But with the steam a great number of other volatile materials
frequently make their appearance. Though we have named a number of these
at the beginning of this chapter, it will not be out of order to
repeat them here. The chief among these are the acid gases known as
hydrochloric acid, sulphurous acid, sulphuretted hydrogen, carbonic
acid, and boracic acid; and with these acid gases there issue hydrogen,
nitrogen ammonia, the volatile metals arsenic, antimony, and mercury,
and some other substances. These volatile substances react upon one
another, and many new compounds are thus formed. By the action of
sulphurous acid and sulphuretted hydrogen on each other, the sulphur
so common in volcanic districts is separated and deposited.
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